Method for making insulated electrical conductors



Nov. 19, 1929.

METHODFORMAKING INSULATED ELECTRICAL CONDUCTORS origi al Filed Au 5, 1924 INVENTOR.

A TTORNEY.

T. HUESTHS I 1,736,444-

Patented Nov. 19, 1929 l UNITED STATES PATENT OFFICE THOMAS B. HUESTIS, OF BRISTOL, RHODE ISLANJ D, ASSIGNOR TO NATIONAL INDIA RUBBER COMPANY, ISLAND OF BRISTOL, RHODE ISLAND, A CORPORATION OF BHODE METHOD FOR MAKING INSULATED ELECTRICAL CONDUCTORS Original application me August 5, 1924-, Serial No. 730,139. Divided and this application filed March 31,

1926. Serial No, 98,655.

- This invention relatesto a method for making insulated electrical conductors, more particularly to a method for compacting such conductors when used in finished form either '6' with or without an outer sheath of soft metal.

while in other cases it is run through a sec-V 0nd tubing machine or lead press .by which it is iven an additional covering or sheath of so t metal such as lead before curing. In some instances the lead sheath ma as a permanent covering-while in ot er cases it is used merely during the cure and is then stripped from the conductor. There are a number of objections to conductors made as above described. The .insulating material deposited by the tubing machine frequently does not come into intimate contact and union with all parts of the conductors which it surrounds, particularly if they are in twisted form or are covered'with Woven or other fabric, and it is not dense enough to rovide the greatest di-electric strength for t e particular material used. When the conductor is to'be surrounded by a lead sheathing it is necessary to incline the tubing die of the lead press in the direction in which the c6nductor passes through it, as otherwise by reason of the great pressure onthe lead it conductor and cause the latter to stick.

Hence as the lead sheath is not applied in a direction normal to the axis of the conduc tor it does not fit as 'closelyas is desired. Moreover, the lead sheath as it issues from the die is of a more or less wavy character with variationin its diameter, and when large cables which have been sheathed in this manner are cured, blisters frequently debe left velop in the insulation on account of the loose fit of the sheath. By reason of the manner of forming the final coat of insulation, or both this insulation and the outer metal sheath, the complete conductor not only varice in diameter but-is not of a minimum cross-section for the amountof material used in its construction. It is evident thatwhere conductors are strung in conduits it is particularly desirable to have them ofa minimum cross-sectional area in order that the greatest number of conductors may be accommodated in the conduit.

An object of my invention is to provide a method by which more dense and perfect insulation maybe disposed on electrical conductors and more perfectly united to them.

Another object is to provide a method by which the cross-sectional area of an insulated conductor of given capacity and variety may be reduced to a minimum.

Still another object is to provide a method by which the formation of blisters in vulcanizable insulation during the curing process may be prevented' The invention consists broadly in closely compacting the outer insulating covering of an electrical conductor, whether surrounded I .or not in final form by a soft metal sheath,

by exerting a relatively heav pressure normally and radially of the con uctor.

1 For a detailed disclosure of the nature and objects of the invention reference is had to the accompanying drawings, in which latter- I Figure 1 is a perspective view of an insul'ated conductor.

Figure 2 is a similar perspective showing the insulated conductor before and after compressing.

would tend to flow backwardly along the with an outer covering 4 of plastic insula- 100 1 p tion by passage through a tubing machine. The covering a is in turn surrounded by a sheath 5 of soft metal such as lead which -may be deposited by means of a tubing machine or lead press. As shown in Figures 1 and 2, the covering 4: of plastic insulation,

which may be a rubber compound containing sulphur, does not fit closely as ordinarily made around the twisted insulated conductors, an open space occurring between them. The lead tubing also'has a loose fit around the plastic insulation in ordinary processes of manufacture.

' fitting layers of material.

To remedy this condition it have provided a method-of compacting the insulated conductor thus formed whereby there is pro duced a product consisting of dense close- An example-of a suitableapparatus for carrying on this invention is shown and described in my copending application, Serial No. 730,139, filed August 5, 1924:, of which this application is a division and reference may be had to that application for a description of the apparatus. A suitable apparatus comprises a plurality of hammers so mounted that they can be driven with considerable force in a series of blowsjagainst the assing conductor. The strilnng faces of te hammers are concave in shape and they operate to compress substantially a complete circumference of the conductor at one time. The resulting compressed conductor retains its cylindrical .the length of which has been passed through for carrying out the present invention ad jacent the lead tuber and to run the sheathed conductor directly from the tuber into thecompacting apparatus. -While the conductor is passed through the compacting device, the concaved faces of the hammers strilre 'a sectionv of the lead-sheathing and compact the conductor to a minimum and uniform diameter. This operation is repeated on successive sections until the entire conductor is compacted. The com acted insu lated conductor is then preferab y subjected to vulcanization whereby the strength of the rubber insulation is increased. If desired,

' the lead'sheath may be retained around the.

conductor when it is put into use or it may be removed as shown in Figure a By the old method it is impossible to geta uniformly tight fit of the lead sheathing on the con avaaaaa dense, hard tight-fitting lead sheath of unias shown in Figure 3 with a consequent sav-' ing of lead. At the same time, as shown in Figures 3 and l,- the insulation beneath the lead sheathing is also compacted and rendered dense so that its di-electic-strength is increased, it is more firmly and perfectly united to the conductor or conductors, and in the case of multiple conductor cables a considerably more compact construction is obtained. By the use of the invention, the formation of blisters in the curing of conductorsinsulated with vulcanizable material is also avoided. ln the case of conductors in which the lead sheath is stripped off after v curing the advantages of uniform diameter,

minimum cross-section, smoother surface, non-blistering, increased di-electric strength, and more perfect union with the conductor or conductors are also obtained. While the invention is particularly applicable in the manufacture of conductors having an outer insulating covering of plastic material formed by a tubing operation, it is evident .form diameter and minimum cross-section that, irrespective of the nature and manner of applying the insulation by surrounding the conductor with a lead sheath in the man ner described and then compacting the sheath the insulating material will at the same time be improved for reasons above stated.

The invention is capable of wide application in the manufacture of many forms of electrical conductors such as submarine, park lighting, fire alarm, and single and multiple conductor power and telephone cables, either where the lead sheath is a permanent part of the conductor or is strippedtherefrom after curing. The invention is also of great value in the manufacture of the single or multiple conductor, flexible cables now so widely used in the arts in connection with portable electrical apparatus, since by its use an outer die formed covering of rubber or other insulation can be produced which is dense, wear resist ing, of relatively high di-electric strength, and which is firmly united to the conductor or conductors at all points.

le a specific embodiment of the invention has been disclosed in the presentap plication, it isobvious that it is capable of 1 numerous modifications, and it is not desired to limit it otherwise than asset fdrth in the appended claims.

7 Having thus described I claim and desire to protect by Letters Pat ent is:

1. The method of forming a-rubber insumy invention what ice - of the cab e a normal force simultaneously Signed at Bristol, county of lated cable which comprises'extruding rubber insulation about an assembly of conductors, extruding lead over the insulation, in-

termittently applying to successive portions of the cable a normal force simultaneously applied to all points in a circumference of the cable, and curing. v

2. The method of forming a rubber insulated cable which comprises extruding rubber insulation about anassembly of conduc-v tors, extruding lead over the insulation, intermittentl applying to successive portions applied to all points in a circumference of the cable, curing, and stripping the lead I sheath from the cable.

State of Rhode Island, this 19th day of March, 1926.

Bristol, and

THOMAS B. HUESTIS. t 

